For current model Sequential Electronic Fuel Injection (SEFI) engines, a large effort is required to calibrate fuel injection control to achieve the correct combustion A/F ratio for the engine conditions of cold start and warmup. Calibrations are required for cold fuel enrichment entransient fuel control strategies.
To reduce cold engine hydrocarbon emissions and provide early catalyst light-off, the coordinated strategy for starting with reduced emissions (CSSRE) is applied. To achieve success with the CSSRE strategy, the desired combustion A/F ratio is about 1.04 times stoichiometric (e.g., 1.04*14.55=15.1 A/F ratio). It is difficult to calibrate fuel control to accurately achieve this desired A/F ratio for the pre-catalyst light-off period, because the factors controlling fuel vaporization rates are not predicted.
Several different methods may be utilized to achieve the desired combustion A/F ratio. In a first method, the injection fuel quantity is scheduled with table values as a function of time since start and of the engine coolant temperature. The disadvantage of this method is that the state of gasoline vaporization varies from engine start to start. Injection control utilizing this method generally results in rich A/F ratio.
An improvement to this method is to schedule a fuel injection multiplier which is a function of the engine temperature and the time since engine start. For this method, the base amount of fuel is determined with the mass air flow measurement method of determining the current cylinder air charge. After the oxygen sensor is fully warm, the on-board A/F sensors are available to provide a measurement of exhaust A/F ratio, which is used to correct the fuel injection quantity and provide the proper combustion A/F ratio. However, this feedback information is not available during the first 10-20 seconds after a cold engine start. Furthermore, this method results in rich A/F ratio for good quality gasoline and lean A/F ratio for poor quality gasoline. Thus, emission and driveability results are highly variable for different cold-start conditions.
Thus, there exists a need to accurately predict combustion A/F ratio using as input measured fuel injection quantities and a gasoline vaporization model.